Minor physical anomalies (MPAs) are believed to reflect abnormalities in fetal neuro development. Several studies have shown that schizophrenia patients have more MPAs than normal controls, but little is known about the meaning of this increased rate of MPAs. The current study first attempted to determine whether the increased MPAs are associated with schizophrenia in particular or with psychosis in general. Second, the study tested whether the patients' siblings also show an increased rate of MPAs by assessing MPAs in schizophrenia patients, bipolar manic patients, the siblings from each group of patients, and normal controls. The schizophrenia patients had significantly more MPAs than normal controls and bipolar patients. The rate of MPAs in bi polar patients did not differ from normal controls. This pat tern suggests that MPAs have some degree of specificity to schizophrenia. Both sibling groups had fewer MPAs than the patients, and this difference was significant for the comparison between schizophrenia patients and their siblings. When viewed within a vulnerability-stress model, the results are consistent with the theory that MPAs may reflect early, largely extra-genetic, stressful events.